As far as I know, Header = The assembly covering/interacting with the "top" end of the cylinders. The intake and exhaust manifolds are either attached to, or are a part of, the header.

Could the assembly dealing with the intake/exhaust of a rotary be called a "header?"
In any case, it doesn't matter that there is indeed, a turbo there, or that there is indeed a header there. It wouldn't have even mattered if Taa-kun was stating that the picture in question was not of a rotary engine.
All nismo4life was expressing was that his 787B's turbo was probably red-hot, and then he provided a picture of red-hot objects for comedic effect.
That's all. He could've even used a picture of hot lava, or molten anything. Whatever.
Any way you look at it, Taa-Kun's comment was simply out of line.